lost contacts list and call logs

Hi, Ive lost all my contact list and call logs for no reason ... I know how to backup and retreive it but I want to know why its happenning? Ive also 2 apps not working! avg antivirus and phoneusage ... thanks for your help!

Also do some research, antiviruses are useless on android. The problem with android isnt viruses, its apps on the market that request permissions they dont need. For example, Gas Buddy needs a GPS Signal/Location data. If it were to request access to your contacts then you know it is spyware requesting permissions it does not need.